LDAP users with username containing only integers have trouble when adding them into a LDAP group

Description

LDAP user with full integer name can be added into any OC created groups but if we add those users into LDAP group and sync them with OC, we get the user as OC user but we do not get those users as members of group we assigned before!

Steps to reproduce

1. create a LDAP user with userid: 123
2. create a LDAP group with cn: grp1, memberuid: 123
3. sync LDAP users and groups with OC
4. see members list of group grp1 using occ command

Expected output

• User 123 should be listed

Actual output

• User 123 is not listed

Reproduce the issue with an LDAP user whose userid is 123 and an LDAP group with memberuid: 123, then sync LDAP users and groups with ownCloud. Use the occ command to inspect group grp1; done means user 123 appears in the group's member list.